Car: 2004 6 speed manual.

Issue: car misfires at 7000 rpm under load. Always kinda hesitates for a sec around 5000 rpm.

Work down to car: new fuel pump, coils, plugs, wires. Maf, map, ess and O2 sensor (got off eBay) I put the original upstream O2 back in. De cat with headers original muffler.

Engine on and off: starts no issue cold or hot. Ideal around 800. Revs fast in nutral.

Questions: obd says it runs lean can the sec 02 cause any of these issues? Fuel trim says st numbers get to -20s.

 

The rear o2 cant cause you to run lean. If fuel trims are in -20, you may have a leakng injector the computer is tryingbto trim for. Potentially also someone swapped or miswired primary and secondary injectors.

What are the fuel trims on a warm idle?
Have you done a nvram reset since you changed all those parts?

 

Thank you for the response.

I have done the brake pedal Reset. Is that what you are talking about?

When the car is idol the trims bounce like -3 to +1 but nothing extreme. It only goes lean on the st and only when under load.

 

Hmmmmmm. See if you can pull the spark plugs and check if one rotor is running richer than the other. If one rotor's soark plugs are darker, it points to an injector. If they're equal, that's something else.

The secondary injectors aren't used at idle so you may want to isolate what rpm range the issue presents in. If it is limited to some range, that's further evidence for injector issue.

The front O2 is original right? Has it ever given you trouble?

 

I did put back the original front o2 sensor. The issues is only once it gets to 5k rpm. It will hesitate then at 7k pick up fast then start to mis fire.

At idle cold

Ideal at warm

Old plugs

 

The front o2 is the original with the car. It starts around 5k at 7 it almost feels like it hits a power band. It starts to move. Then shortly after it will misfire. Maybe the motor is going.

 

If it's misfiring you should get a CEL and a code.

 

P 0302

 

It's not the motor. That not how loss of compression manifests.
Betwern 5 and 7k is about where the secondary injectors kick in but tertiaries are not yet on.
Possible the secondaries or tertiaries are overfueling for some reason.

Have a read/look here https://www.rx8club.com/series-i-tec...em-work-81477/

Possible your secondary shutter valve is sticking as well, that would limit intake airflow in that range. There is usually a code for this though.

 

Thank you for the information. My ssv opens and closes easy even checked with a pump. I did replace all three Solenoids. Maybe I have a clogged or bad injector. I do appreciate the help took two years to get to this point. Just wish I can figure this out.

 

So I put new injectors on it, runs better does not hesitate like it use to however it still has a misfire under load.

Is the vac at idle supposed to be to be zero? Mine sits around -2.

 

-2 what?

It should definitely not be close to 0. Sounds like you have air getting in somewhere after the throttle body.

 

Just Incase anyone reads this replacing the injectors seemed to help but now my vdi is staying open.

 

-2 psi. That’s on the app I use. Maybe it’s not that accurate.

 

There's no MAP sensor on our cars so DashCommand must be guessing at what the pressure is.

If you're getting hesitation in mid-/upper-RPM, I wonder if one or more of your solenoids is bad. I know you said you replaced them but have you tested the new ones? Get a MityVac hand pump and pull 10 psi vacuum on the port that connects to the vacuum accumulator (the lone port opposite the connector). If it holds vacuum, apply 12V across the pins (polarity shouldn't matter since it's just energizing a coil). The vacuum should immediately go away. If that works fine, test the check valve between the accumulator and the UIM.

The same goes with the coils. You said they are new but that doesn't mean that they are working perfectly. Get an HEI coil tester (the $20 one on Amazon works well).

 

hello, i just bought a rx8 cosmo of 2005 with rebuilt engine and everything is replaced ( wires , coils and spark plugs) but it doesn't have thermostat .
i but an obd 2 and it shows me that i have 2 codes p0300 whitch is misfire and p0850 for park/neutral swich seanson ( destroyed) and i want to if there are connectied those 2 codes ?
i have check the sensors ess and maf and ther are ok !